1. Field of the Invention
This invention generally relates to a technique of fabricating display panels, and more specifically, to a fabrication method for a display panel with a dielectric configuration applied thereto.
2. Description of Related Art
Liquid crystal display (LCD) technology is rapidly replacing conventional cathode ray tube (CRT) technology in the market. Compared with heavy and bulky CRT displays, liquid crystal displays have many obvious advantages, such as being lightweight, having lower power consumption, emitting less radiation, and possessing soft and clear images, and have thus become popular with consumers. Nevertheless, it is still desirable to enhance the product quality and lower production costs, and each manufacturer is looking for a technological edge in the market.
In the process of manufacturing display panels, liquid crystal filling and end-sealing are essential procedures for filling in the dielectric, such as liquid crystal. The vacuum liquid crystal filling technique and one drop filling (ODF) technique are two presently applied modes of fabricating liquid crystal panels.
In the vacuum liquid crystal filling technique, first, a few sheets of upper and lower substrates are precisely aligned and abutted to each other, forming openings for filling liquid crystal therein. Next, this batch of aligned and abutted panels is placed on a processing utensil, and the panels and utensil are put inside a vacuum chamber along with a liquid crystal bath. Then, after the vacuum chamber is in a complete vacuum state, the panels are submerged in the liquid crystal bath to fill-in the liquid crystal openings. Afterwards, dry air is brought into the enclosed vacuum chamber, thereby taking the enclosed chamber back up to standard atmospheric pressure. Accordingly, by way of capillary action and pressure differences, liquid crystal is gradually introduced into the gaps or openings of the panels. Then, after the enclosed vacuum chamber has been gradually brought back to normal atmospheric pressure, the panels are removed. However, in the process, bulges will often form on surface of the panels after crystal liquid is introduced into the gaps, and so a flatting process must be applied. After the flatting process, excess liquid crystal is wiped away, and then a sealant is applied to seal up the openings, thus completing the process.
However, this vacuum liquid crystal filling technique takes a long time to complete the full process. Moreover, the process not only consumes a large amount of liquid crystal, but also wastes the excess liquid crystal between the panels. In addition, capillary action is not strong enough to fill-in small cell gaps of the panels. In addition to these drawbacks, the process is not ideally suited to achieve the demands of fabricating larger-scale panels. Furthermore, the equipment required for processing in a vacuum environment is very expensive. There are also additional difficulties in the operational procedures of this fabrication technique. In summary, with the disadvantages of a time-consuming fabrication process, high production costs, and low production yield, the above conventional process has limited application scope.
Referring to the one drop filling technique, there are some advantages compared to the vacuum liquid crystal filling technique. The one drop filling technique has a less time-consuming fabrication process, consumes less liquid crystal, and exhibits a higher production yield. Also, small cell gaps of the panels are better filled by use of a spacer and the process is more applicable to the fabrication demands of large size panels. In the one drop filling fabrication technique, first, a sealant is dispensed on the lower substrate to restrict the area in which liquid crystal is allowed to run/flow. Next, an appropriate amount of liquid crystal is dropped in. Then, after the fabrication process applied to the lower substrate is complete, the upper substrate and lower substrate are placed in a vacuum environment, wherein a high precision aligning and pressing process is conducted and ultraviolet rays are applied for curing, thus completing the process of liquid crystal filling and end-sealing.
FIGS. 1A and 1B illustrate a fabrication method for a liquid crystal device according to U.S. Pat. No. 5,978,065. Referring to FIGS. 1A and 1B, first an upper substrate 1 and a lower substrate 2 are provided, and a plurality of spacers (not shown) are arranged between the upper and the lower substrates 1 and 2. These spacers provide a means of forming gaps between the upper and the lower substrates 1 and 2. Then, in the process of filling-in dielectric, liquid crystal 3 is applied on the lower substrate in an irregular pattern. Finally, the upper substrate 1 is pressed on to the lower substrate 2 by first rolling and pressing over the upper substrate 1 with a thermal pressing roller 4a, and then pressing two more times by rolling and pressing with two auxiliary pressure rollers 4b and 4c in an effort to control the pressure applied to the upper and the lower substrates 1 and 2.
However, in the actual operational process, the pressure applied by the thermal pressing roller is unlikely to be well controlled. If the pressure is too low, the liquid crystal will not be dispersed adequately, resulting in unevenness. If the pressure is too high, the spacers are likely to be crushed, and consequently cause damage to the substrate. Moreover, since the dropped liquid crystal is in an irregular pattern, a curved wave front behavior is likely to occur in the liquid crystal material while the thermal pressing roller is running over the substrate, and bubbles in the liquid crystal are consequently produced, thereby lowering production yield.
FIGS. 2A and 2B illustrate another fabrication method for a liquid crystal display panel according to the disclosure of U.S. Pat. No. 6,734,943. As shown in the FIGS., the technique of the patent provides an upper substrate 11, a lower substrate 10, and a plurality of spacers between the upper substrate 11 and the lower substrate 10, wherein the spacers are for providing gaps between the upper substrate 11 and the lower substrate 10. Also, the sealant 101 is dispensed along the periphery of the coating region of the lower substrate 10, and a plurality of air outlets 102 are preset in the sealant. In the process of filling in liquid crystal, first, a layer of liquid crystal 3 is dropped on top of the lower substrate 10. Then, the upper substrate 11 and the lower substrate 10 are placed together and pressure is applied to squeeze out air bubbles in the liquid crystal between the upper substrate 11 and the lower substrate 10 via the plurality of air outlets 102. However, in this method of dispersing the liquid crystal between the upper and the lower substrates by means of squeezing, the required amount of liquid crystal must be pre-calculated quite precisely, and the process also must be conducted in a vacuum environment, thereby increasing not only the production costs but also operational difficulties.
Furthermore, although both of the two aforesaid techniques for filling-in liquid crystal are conducted in a strictly controlled vacuum environment, the air bubble problem cannot be avoided completely; and since vacuum equipment is essential, high production costs is unavoidable. Also, the strict control necessary to ensure a complete vacuum environment causes difficulties in application. In addition, for future application to related products, such as flexible displays, electronic books, polymer panels, and others, the production cost is certain to remain high while the yield is low, thereby limiting applicability in the industry.
Hence, it is a critical issue in the industry to develop a method to fabricate display panels at atmospheric pressure that can effectively solve the drawbacks of the prior arts as mentioned above.